We investigate the spectroscopic characteristics of the optical
components of Be/X-ray binary systems, using data collected during our
seven-year monitoring campaign. We find examples of major changes in
the emission line profiles associated with Type II X-ray outbursts,
later developing into V/R variability cycles. We show that the
time-scales for V/R variability in Be/X-ray transients extend from a
few weeks to years and interpret all these changes as due to the
presence of global disruptions of the axisymmetric density
distribution in the extended envelopes of the Be stars in these
systems. The association between X-ray outbursts and V/R variability,
the occurrence of very fast changes and the very short quasi-periods
of variability displayed by Be/X-ray binaries lead us to conclude that
the presence of the neutron star is an important factor affecting the
dynamics of the disc-like envelopes. The interaction between the
compact companion and the disc would explain the correlation between
H strength and orbital period recently found. The
characteristics of the V/R cycles are, however, mainly independent of
the binary parameters.